Ok, feel like I missed a lot here, as I don't get some of the references, and I am up to date on the books
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What is the significance of Horus at Molech (What/when/where is Molech?)
I thought Horus started losing as soon as his super-saiyan arrogance was ignited in the fever dream on Davin, or when he started listening to Erebus (where the hell has he been since book 2?) BUT, the Emperor did not help the issue, by unexplainedly withdrawing from his sons to create the opening in the webway that Maguns promptly fooked up in his hubris.
Had Woody only gone to the police......

Molech holds a doorway to the Warp, that the Emperor used to take the fight to the Ruinous Powers and in so doing, achieve his current level of divinity. Horus invaded that world basically to prove himself to his new masters, and to do about 10,000 years of power-leveling in the Warp. As for Erebus, he and Space Falwell and Space Graham were busy beating up Smurfs (Know No Fear, Mark of Calth), trying to kill the Emperor (Nemesis, Vulkan Lives), trying to keep the Angels out of the fight/turn Sanguinius (Fear to Tread) and turning Angron into the first officially recognized Daemon Prince (Betrayer, although arguments can be made both for Magnus, as the Scourging of Prospero happened around the same time as the battle of Isstvan IV, and Fulgrim, whose apotheosis occurred a few months after the Dropsite Massacre, in Angel Exterminatus).

ok, now I'm more confused lol.
I thought the Big E is a psychic construct from the life force of 'ancient shamans' and pretty much came to life as a divine being.
Molech is still not ringing a bell, as I don't recall the Emp 'taking the fight to the Ruinous Powers'. I thought the only time he fought Chaos directly was when Magnus screwed 'THE PLAN' by destroying the barrier on the broken webway portal in da Throne Room....
Any sources on the above comments?
Also I don't remember Horus entering the warp to power up... I thought he was mainly resistant to the Powers due to his own vainglorious nature and hubris.
The other sources quoted by Andrew I do remember (awesome job pinpointing those events, btw!)

ok, now I'm more confused lol.
I thought the Big E is a psychic construct from the life force of 'ancient shamans' and pretty much came to life as a divine being.
Molech is still not ringing a bell, as I don't recall the Emp 'taking the fight to the Ruinous Powers'. I thought the only time he fought Chaos directly was when Magnus screwed 'THE PLAN' by destroying the barrier on the broken webway portal in da Throne Room....
Any sources on the above comments?
Also I don't remember Horus entering the warp to power up... I thought he was mainly resistant to the Powers due to his own vainglorious nature and hubris.
The other sources quoted by Andrew I do remember (awesome job pinpointing those events, btw!)

No idea where the Shamans thing came from, although I saw the Lexicanum article. Much of the more recent Horus Heresy books would make it seem that the Emperor is just another Perpetual, one that was not content with being a pawn in the Eldar scheme to destroy the Ruinous Powers. At least, that's how I headcanon it.

The Molech story is the main plot in Vengeful Spirit. Horus, Fulgrim, and Mortarion lay siege to the Knight world of Molech in order to find a portal to the Warp used by the Emperor relatively early in human history, supposedly prior to the establishment of House Devine as its guardians, to physically enter the Immaterium. After turning House Devine and obliterating the Molech's defenders, by blowing up an Emperor-class Titan and unleashing Grulgor and the Red Angel, the three Primarchs found the Portal, Horus entered, and over the course of an hour, experienced 10,000 years of War within the Warp, and, having curried favor with the Powers, emerged empowered but still mostly a normal Primarch. This differed from how the Emperor did it in that Horus was neither a natural Psyker nor was he a Perpetual, and in that he accepted the rewards and privileges extended him by the Gods where the Emperor rejected them. What's odd, but fitting considering that the 7th edition Knight codex was published around the same time, was that in the book, no one, not even the Primarchs present, had exact memories as to why Molech was so important as to warrant the garrison of 3 Knight Households, a Titan Legio, and a Company of Blood Angels, only that it was an important world, echoing the retcons in both Knight Codexes that attempted to explain that Knights were always part of the 40k setting, despite only ever existing on the tabletop as early Epic 40k models.

Oh waitasec - Molech IS where Knight House Adam Devine was established, the obvious but shhhhhh eventual followers of Slaanesh. They appeared in a short story as well, something to do with one of the sons of House Device becoming an incubator for a demon while sequestered in the hold of a space ship.......I dunno, can't remember much detail, but they were all SURPRISE Slaanesh worshipers, and there was a young orphaned girl involved with a pre-Grey Knight Errant of Malcador.......
There's a lore story for Big E, might even be the short story 'The Last Church' or in Horus Rising, as indeed, the Big E is a divine construct made of the life force of all of earth's shamans, from, like, waaaaaaaaaaaay back when (allegedly, before recorded history, He has been around since Shamans were shamans, but bide His time until he could reveal Himself).
I am gonna have to read Vengeful Spirit again, cuz I don't remember any of this lol.
Side thought: wasn't a female inquisitor turned in to the Red Angel in the Ultramarines Omnibus, through Daemonica Speculum (can't remember the name for $#!t). in your post, are you referencing Angron as the Red Angel? Crapo, I really need to reread the book. I believe the Red Angel is also used to describe Sanguinius, as well as one particular demon, and Angron, and the converted female character I mentioned: she goes on to destroy a whole OTHER FRIKKIN UNKNOWN GALAXY BY HERSELF/ITSELF and then reappears after this heretofore unknown carnage like 'hey, whatsup?'
I believe ALL primarchs have some level of psychic powers, be it from an aura of control to outright psychic shenanigans..... that they could even sense each other psychically...
Yeah, ur post is great, mine sounds like a 3rd grade book report...

Oh waitasec - Molech IS where Knight House Adam Devine was established, the obvious but shhhhhh eventual followers of Slaanesh. They appeared in a short story as well, something to do with one of the sons of House Device becoming an incubator for a demon while sequestered in the hold of a space ship.......I dunno, can't remember much detail, but they were all SURPRISE Slaanesh worshipers, and there was a young orphaned girl involved with a pre-Grey Knight Errant of Malcador.......
There's a lore story for Big E, might even be the short story 'The Last Church' or in Horus Rising, as indeed, the Big E is a divine construct made of the life force of all of earth's shamans, from, like, waaaaaaaaaaaay back when (allegedly, before recorded history, He has been around since Shamans were shamans, but bide His time until he could reveal Himself).
I am gonna have to read Vengeful Spirit again, cuz I don't remember any of this lol.
Side thought: wasn't a female inquisitor turned in to the Red Angel in the Ultramarines Omnibus, through Daemonica Speculum (can't remember the name for $#!t). in your post, are you referencing Angron as the Red Angel? Crapo, I really need to reread the book. I believe the Red Angel is also used to describe Sanguinius, as well as one particular demon, and Angron, and the converted female character I mentioned: she goes on to destroy a whole OTHER FRIKKIN UNKNOWN GALAXY BY HERSELF/ITSELF and then reappears after this heretofore unknown carnage like 'hey, whatsup?'
I believe ALL primarchs have some level of psychic powers, be it from an aura of control to outright psychic shenanigans..... that they could even sense each other psychically...
Yeah, ur post is great, mine sounds like a 3rd grade book report...